An optical film typified by a polarizer protective film for protecting a polarizer or a film substrate for liquid crystal display is required to have optical transparency and optical homogeneity.
As a method for manufacturing such an optical film, a melt extrusion method is known in which a resin composition as a film raw material is melted in a melt extruder and extruded from a die in film form to form a film. Further, a film molding method is known in which a film-shaped molten resin extruded from a die by such a melt extrusion method is inserted between a pair of smoothing rollers in order to reduce the thickness variation or surface irregularities of the film and to improve the surface smoothness of the film (see PTL 1 and PTL 2).